1. Field of the Invention
This invention is related to downhole tools for a hydrocarbon wellbore. More particularly, the invention relates to an apparatus useful in conducting a fracturing or other wellbore treating operation. More particularly still, this invention relates to a filtered inlet port through which a wellbore treating fluid such as a “frac” fluid may be pumped without obstructing the workings of a hydraulic tool.
2. Description of the Related Art
In the drilling of oil and gas wells, a wellbore is formed using a drill bit that is urged downwardly at a lower end of a drill string. When the well is drilled to a first designated depth, a first string of casing is run into the wellbore. The first string of casing is hung from the surface, and then cement is circulated into the annulus behind the casing. Typically, the well is drilled to a second designated depth after the first string of casing is set in the wellbore. A second string of casing, or liner, is run into the wellbore to the second designated depth. This process may be repeated with additional liner strings until the well has been drilled to total depth. In this manner, wells are typically formed with two or more strings of casing having an ever-decreasing diameter.
After a well has been drilled, it is desirable to provide a flow path for hydrocarbons from the surrounding formation into the newly formed wellbore. Therefore, after all casing has been set, perforations are shot through the liner string at a depth which equates to the anticipated depth of hydrocarbons. Alternatively, a liner having pre-formed slots may be run into the hole as casing. Alternatively still, a lower portion of the wellbore may remain uncased so that the formation and fluids residing therein remain exposed to the wellbore.
In many instances, either before or after production has begun, it is desirable to inject a treating fluid into the surrounding formation at particular depths. Such a depth is sometimes referred to as “an area of interest” in a formation. Various treating fluids are known, such as acids, polymers, and fracturing fluids.
In order to treat an area of interest, it is desirable to “straddle” the area of interest within the wellbore. This is typically done by “packing off” the wellbore above and below the area of interest. To accomplish this, a first packer having a packing element is set above the area of interest, and a second packer also having a packing element is set below the area of interest. Treating fluids can then be injected under pressure into the formation between the two set packers.
A variety of pack-off tools are available which include two selectively-settable and spaced-apart packing elements. Several such prior art tools use a piston or pistons movable in response to hydraulic pressure in order to actuate the setting apparatus for the packing elements. However, debris or other material can block or clog the piston apparatus, inhibiting or preventing setting of the packing elements. Such debris can also prevent the un-setting or release of the packing elements. This is particularly true during fracturing operations, or “frac jobs,” which utilize sand or granular aggregate as part of the formation treatment fluid.
Prior solutions to the debris problem have included running in a filter or screen above the down-hole tool. This has several disadvantages. First, once the screen is run above the down-hole tool, full pressure can no longer be transmitted to the piston. Second, emergency release mechanisms and other devices actuated by a ball cannot be used.
There is, therefore, a need for a hydraulic down-hole tool which does not require a piston susceptible to becoming clogged by sand or other debris.